1. Field of the Invention
The present invention relates to an image display apparatus. The image display apparatus according to the present invention is suitable for, for example, a head-mounted display (HMD) and eyeglass displays.
2. Description of the Related Art
Various image viewing apparatuses (image display apparatuses) that are worn on the head and allow image information displayed on an image display device (e.g., liquid-crystal display device) to be viewed as an enlarged virtual image, so-called head-mounted displays (HMDs), have been proposed.
Head-mounted image display apparatuses need to allow a viewer to view a realistic image with a wide angle of view and have a compact lightweight structure.
Among such apparatuses, a HMD that uses a reflective liquid-crystal display device is known (see, for example, Japanese Patent Laid-Open No. 2001-166252, No. 11-125791 (corresponding to U.S. Pat. No. 6,333,820), No. 11-337863 (corresponding to U.S. Pat. No. 6,023,373), No. 2000-010041, and No. 2002-244076 (corresponding to U.S. Pat. No. 7,081,999).
With recent advances in high-definition liquid-crystal display devices, liquid-crystal display devices that have as many pixels as, or even more than, existing displays while at the same time being more miniaturized than existing displays are being developed.
In order to enable a realistic image with a wider angle of view to be displayed using a miniaturized liquid-crystal display device, it is necessary to increase the magnification of a display optical system. However, an increase in magnification leads to an increase in size of the optical system, and inevitably, this tends to an increase in the size of the entire structure of the apparatus.
To miniaturize the optical system while attaining a wide angle of view and enabling display of a high-definition image, an effective way is to use a decentered optical system including an optical element that has a rotationally asymmetric surface.
However, the use of a decentered optical system is prone to cause luminance non-uniformity in an image viewed at an exit pupil of the display optical system.
Additionally, the ratio of light incident on the exit pupil at a viewer side to light that has been optically modulated by a liquid-crystal display device after having emerged from an illumination unit is reduced, and the efficiency of illumination tends to be decreased.
Therefore, in order to miniaturize the entire optical system and also enable a high-definition image with a wide angle of view to be obtained, an important factor is to appropriately set the structure of an illumination optical system for illuminating a liquid-crystal display device and the structure of a display optical system that guides light from the liquid-crystal display device to an exit pupil at a viewer side.